Evaluation of effect of three different dental unit waterline antimicrobials on the shear bond strength to dentin - An ex vivo study.

BACKGROUND: In restorative treatment dental unit water is used while irrigating the cavity and also in the use of composite restorations to flush away the etchant to place bonding agent. These antimicrobials may influence the bond strength of the dentine bonding agent to the dentine. AIM AND
OBJECTIVE: To evaluate the effect of three different dental units waterline antimicrobials on the shear bond strength of dentin.
MATERIALS AND METHODS: Sixty freshly extracted human teeth were taken and the occlusal surfaces were sectioned to obtain a flat dentin surface. Then the teeth were randomized into 4 groups depending on the antimicrobial used: Group 1(Distilled water), Group 2 (Alpron), Group 3 (CitriSil), and Group 4 (Chlorhexidine). The dentine surface was prepared for bonding and composite resin was placed in two increments of 2 mm each. The specimens were stored in distilled water, thermo cycled after 7 days shear test was performed by using the universal testing machine. RESULT: No significant difference between Group 1 and Group 2 with regard to shear bond strength. There was a significant difference in the SBS of Group 1 and Group 3 and Group 4. The SBS of group 2 was higher than Group 3 and Group 4 and the difference was statistically significant.
CONCLUSION: Citrisil and Chlorhexidine groups showed affected bond strength whereas Alpron did not vary with bond strength.

INTRODUCTION

Dental unit waterlines (DUWL) are an integral part of the dental equipment, supplying water for high speed handpieces, ultrasonic scalers and air/water syringes. It has been found that the DUWL is contaminated by many species of microorganisms; the source of the microorganism to these waterlines is the passive retraction of the oral fluids when the equipment is turned off.[1]

Within the DUWL it is found that there are microcolonies of proliferating bacteria, viruses and fungi.[2] Another problem associated with DUWL is the formation of biofilms. Thus these microbes in the biofilm can form a continuous source of infection to the dentists as well as patients.[3] The research on DUWL clearly shows a high degree of contamination and the need to decontaminate the lines with an antimicrobial.[4]

Various methods of disinfecting the DUWL have been employed such as flushing, filtration, use of anti-retraction valves, use of an independent reservoir, use of chemical disinfectants, electrochemically treated water, autoclavable systems, etc.[5] Some of the chemical disinfectants that can be used to clean the DUWL are Blutab, Bioblue, Sodium hypochlorite, Mouthwashes, Alpron, Citrisil, etc.[6] It has been demonstrated that though the total viable count is reduced using chemical disinfectant, the biofilms are not completely eliminated.

In the total etch and rinse systems, bonding of the composite involves two step, the use of conditioner or etchant [orthophosphoric acid] followed by rinsing of the cavity with copious amounts of water provided by the DUWL. This procedure is followed by application of a dentin bonding agent.[7]

There is wide range of commercial intermittent and continuous chemical treatments for dental unit waterlines. If a continuous chemical treatment regimen is used in the dental unit waterline it could probably remain on the cavity after extensive rinsing either after etching as in total etch or after rinsing or during cavity preparation as in self-etch adhesive system, and could influence the bond strength of dentin bonding agent to the dentine. There is no univocal consensus with respect to the disinfectants used in DUWL and their effect on the bond strength to dentin.[8-13]

Alpron, citirsil and chlorhexidine are continuously used antimicrobials of the DUWL. Literature does not show many studies done on these antimicrobials’ effect on the shear bond strength of dentin bonding agent. Hence, the present study aims to test the hypothesis, if any, on the effect of various DUWL antimicrobials on shear bond strength of dentine bonding agent.

MATERIALS AND METHODS

Sixty third molars extracted for periodontal, prosthetic reasons were selected and handled as per OSHA and CDC regulations.

The occlusal surfaces of the teeth were removed by sectioning them using a water-cooled carborundum disk. The teeth were then mounted in an autopolymerizing acrylic resin using cylindrical PVC molds of 25-mm length and 20-mm diameter. The teeth were so positioned that the prepared dentinal surfaces were 2 mm above the end of resin cylinder.

The specimens were randomized into 4 groups of 15 each depending on the antimicrobial used: Group 1: Distilled water- CONTROL, Group 2: Alpron (Biguanide and EDTA), Group 3: CitriSil (Citric acid) and Group 4: Chlorhexidine (Bisbiguanide).

Thirt-seven percent phosphoric acid (DENTAL MANUFACTURER, USA) was applied on the occlusal surface of the specimen for 15 seconds, rinsing was done as follows.

In group 1, Distilled water was used. After the etchant was placed for 15 seconds it was thoroughly rinsed with distilled water. The distilled water was drawn in a 50 ml of syringe and injected on the surface of the specimen for 15 seconds.

In group 2, Alpron was used. The DUWL antimicrobial was prepared according to the manufacturer's instruction. The concentrated liquid of Alpron was diluted in the distilled water as directed. A 10 ml of the solution was added to 990 ml of distilled water. In this group, a 50 ml of the solution was drawn in a 50 ml of syringe and injected on the surface of the specimen for 15 seconds.

In group 3, the DUWL antimicrobial used was Citrisil. In this group the antimicrobial was prepared by dissolving a single tablet of Citrisil in 1000 ml of distilled water as instructed by the manufacturer. Then 50 ml of the solution was drawn in a 50 ml of syringe and injected on the surface of the specimen for 15 seconds.

In group 4, 0.2% of chlorhexidine was used. A 50 ml of the solution was drawn in a 50 ml of syringe and injected on the surface of the specimen for 15 seconds.

Immediately after etching and rinsing with the DUWL cleansers depending on each group, each specimen was coated with two consecutive coats of dentine bonding agent ADPER SINGLE BOND PLUS ADHESIVE (3M ESPE, US). Using LED [3M] light source it was light cured for 40 seconds. A split Teflon mould measuring 4 × 4 mm was taken. This served as a template, which was placed on the occlusal surface of the teeth. Z 100 A2 shade (3M) composite resin was used, and was placed in the mould space in increments of 2 mm and cured.

The four groups were separately stored in distilled water for 48 hours. The specimens were thermocycled in water baths at temperatures of −5° and 55°C, with a dwell time of 20 sec and a transfer time of 4 seconds. Two hundred and fifty cycles were completed for each group and later they were stored in distilled water for 7 days.

At the end of 7 days, Universal testing machine, Zwick Hoeller was used to study the bond strength at a crosshead speed of 0.5 mm/min, and a max force of 2 kN. The force was applied till the composite gave way. The maximum force required to fracture was recorded for all the specimens.

One way analysis of variance was conducted to compare the bond strength between the groups and intergroup comparison was performed with the post hoc Bonferroni test”. The P value <0.05 considered as statistically significant.

RESULTS

Thus the shear bond strength of group 2(Alpron) is higher compared to all the groups, followed by group 1(Control), group 4 (CHX) and group 3(Citrisil) and there is variance in shear bond strength to dentin Table 1.

Table 1

Comparison of mean shear bond strength (Mpa)

In the Table 2 where the student t test is applied to study if there was any significant difference with individual groups:

Table 2

Intergroup comparison of shear bond strength

When the control group, group 1 is compared with the other groups, it is found that there is no significant difference between the group 1 and group 2 (Alpron) (P>0.05). There is a significant difference in bond strength between group 1 and the other two groups i.e., group 3 (Citrisil) and group 4 (CHX) (P<0.05)

When the grou 2 (Alpron) is compared with group 3 (Citrisil) and group 4 (CHX), there is a significant difference in the bond strength (P<0.05)

When the group 3 (Citrisil) is compared with group 4 (CHX) the P value is 0.980, hence there is no significant difference between the group 3 (Citrisil) and group 4 (CHX).

DISCUSSION

In this study there were four groups, depending on the DUWL antimicrobial used as the irrigant to rinse the phosphoric acid etchant, before placing the dentin bonding agent and the composite. A possible influence on the dentin bond strength was hypothesized as due to the composition of the antimicrobial or disinfectant solution.

The result of the present study with regard to group 2 (Alpron) was in agreement with Betke et al.[7] Here the authors studied the influence of water disinfectants used in dental unit waterlines on the dentin bonding of different adhesive systems using push-out tests. The disinfectants used were Alpron mint, Alpron neutral and Dentosept, and the results showed no significant influence on the loads required for debonding of Syntac Classic, Clearfil Liner Bond 2V and OptiBond FL as compared to the controls.

It was also observed that group 2 (Alpron) exhibited higher maximum bond strength of upto 26.87 MPa when compared to the control, and the minimum bond strength was 13.53 MPa. The data of this group demonstrated a variable result and showed a greatest range in dentin SBS values. Possible cause for this variation in the bond strength could be due to differences in the quality of the dentin among the tooth samples, the bonding methodology or the interaction between the components of the antimicrobial and the dentin surface.[12]

One of the constituents of group3 (Citrisil) is sodium citrate which forms citric acid when dissolved and also it is speculated that the silver constituent could probably influence in decreasing the bond strength and another factor could be attributed to the interaction of the antimicrobials with either the conditioned dentin or the dentin bonding agent and relative acidity of the citric acid.

A similar report was observed in a study by Roberts et al.[10] who tested effects on dentin bond strength of four DUWL disinfectants. They found that all antimicrobial agents tested reduced bond strength, and that citric acid containing Bioclear and diluted listerine mouthwash showed significantly lower bond strength relative to the distilled water control.

Group 4 (Chlrohexidine) is a well-known antimicrobial agent which is a Bisbiguanide. It has a broad sprectrum and is effective against a wide range of microorganism.[13] It is used as a mouth rinse and also as irrigant and disinfectant of the root canals.[1415] Mouth rinses in low concentrations have been evaluated as DUWL cleansers. Chlorhexidine in the concentration of 2, 0.2 and 0.12% have been evaluated as effective DUWL antimicrobials.[16]

Taylor-Hardy and colleagues[17] also reported that 0.12% chlorhexidine gluconate reduced enamel bond strengths compared with the distilled water.

The result obtained in the group 4 (chlorhexidine) was in agreement with various studies which demonstrate lower bond strength with the use of chlorhexidine. However, there are controversial results in literature regarding chlorhexidine.[718] The use of CHX as a preparation disinfectant or cavity cleanser has reported not to affect the bond strength when All Bond 2 and Tenure was used.[19] In fact, other studies have found that chlorhexidine had no effect on dentin bond strength.[2021]

The properties of dentin are important in understanding adhesion of dentin. Adhesive systems bond strength values to dentin may change due to the location of bonding area, water content and permeability of dentin, which is not identical for all regions because of variations in the number of tubules per mm.[22] The limitation of the study could be because of use of extracted teeth the dentin permeability of each tooth could vary widely could influence the bond strength.

In this study only one bonding agent Adper Single bond and only one composite resin, A2 shade, Z100 was used. Various studies have found differences in the bond strength when different adhesive systems were used and since the main objective of the study was to check the effect of the DUWL antimicrobial than the adhesive systems, only one adhesive was used.

On the basis of the study results, tested DUWL antimicrobial citrisil and chlorhexidine did significantly affect the shear bond strength of dentin bonding agent. Alpron did not affect the bond strength. Thus it can be concluded that the bond strength is dependent on the type of DUWL antimicrobials used.

CONCLUSIONS

The use of DUWL antimicrobials is a less known concept in the Indian scenario, which would probably come up with the regulatory bodies taking further initiatives to introduce this protocol. The tested DUWL antimicrobials citrisil and chlorhexidine did significantly affect the shear bond strength of dentin bonding agent. Alpron did not show any significant affect on bond strength, and performed well when compared to citrisil and chlorhexidine.